A randomized prospective study of the efficacy of routine ultrasound screening is proposed for clinically normal pregnancies in which 5000 women will be assigned to receive routine ultrasound screening and 5000 to receive none or only clinically indicated obstetrical ultrasound. The ultrasound screening will consist of: an ultrasound administered at 16-20 weeks to accurately date the pregnancy and detect multiple gestation, or congenital anomalies and an ultrasound in later pregnancy (32-36 weeks) to detect abnormalities of fetal growth, fetal presentation, and placental or amniotic fluid abnormalities. The efficacy of ultrasound screening to alter a variety of pregnancy endpoints including fetal or neonatal death, neonatal seizures, low birth weight, shoulder dystocia, low apgars, cesarean section, newborn admission to special care, and maternal length of stay will be determined by calculating rate ratios and rate differences for the screened and non-screened group. These measures will be calculated for the entire group as well as for obstetrical subgroups potentially defined prenatally such as twins, breeches, placenta previa, growth retarded, or macrosomic infants. Eligibility for the study as well as risk factors for pregnancy outcome such as maternal age, socioeconomic status, prior obstetrical history, prepregnancy weight and nutrition, active and passive smoking, and occupation will be obtained thr a self administered questionnaire completed prior to ultrasound assignment. This will permit identification of risk factors that operate independent of, modify, or confound the effect of screening using multivariate analysis. Detailed data on cost of outpatient and in-patient maternity care will also be collected to enable any identified benefits of ultrasound to be viewed in perspective of their costs. The results of this study could impact on a number of issues that affect 3.7 million women delivering in this country annually including the cost-effective use of ultrasound, the rate of cesarean section, the occurrence of low birth weight infants, and other causes of intrapartum asphyxia of the newborn. Improved understanding of the risk factors for adverse pregnancy outcomes will contribute to safer obstetrical care.